The invention relates to power trains of motor vehicles in general, and more particularly to improvements in methods of and in apparatus for operating adjustable torque transmitting systems (e.g., in the form of engageable and disengageable friction clutches) of such power trains.
As a rule, or at least in many instances, the operation of the friction clutch in the power train of a motor vehicle (normally but not necessarily between the rotary output element of a prime mover and the rotary input element of a change-speed transmission) is regulated automatically by one or more actuators (e.g., electric motors in conjunction with gearings and/or fluid-operated cylinder and piston units) which receives or receive signals from a computerized control unit. The control unit normally processes signals denoting various operational parameters of the motor vehicle and/or of its power train; and its output signal to the actuator or actuators reflects the intensity or intensities (and/or other characteristics) of the signal or signals being processed by the evaluating circuit or circuits of the control unit.
An advantage of an automatically operated torque transmitting system (hereinafter called clutch or friction clutch for short) is that it contributes considerably to the comfort of the operator and other occupant(s) (if any) of a motor vehicle. Furthermore, the utilization of an automatically engageable and disengageable friction clutch can entail a reduction of fuel consumption, especially when the clutch is connected between the crankshaft or camshaft of an internal combustion engine (such as an Otto engine) and the input shaft of an automated or automatic transmission in the power train of a motor vehicle. Such types of power trains are more likely to ensure an automatic selection of a transmission ratio which is best suited for the transmission of torque to the driven wheels of the motor vehicle, namely which is most likely to ensure a highly economical operation of the engine under the prevailing circumstances of use of the motor vehicle.
In order to reduce the energy consumption of the associated actuator or actuators, as well as to ensure speedy adjustments of the magnitude of transmitted torque, an automated clutch is normally operated in such a way that the extent of its engagement is best suited for operation without slip or without undue (excessive) slip. To this end, it is customary to select the extent of engagement of the clutch as a function of the RPM of the rotary output element of the prime mover, of the RPM of the rotary input element of the transmission (such RPM is normally indicative (or it can be utilized for a determination) of the speed of the motor vehicle), and the load upon the prime mover in such a way that the clutch can transmit a predetermined torque.
However, when the circumstances of use of a motor vehicle depart from normal circumstances, for example, when the vehicle is utilized on mountain roads or elsewhere well above the sea level (turbo engines are particularly sensitive under such circumstances of use), when the outside temperature is very low, and/or under certain other circumstances, it can happen (especially while setting the vehicle in motion) that the disengagement of the clutch is excessive which prevents the engine from reaching an RPM at which it can or could furnish a maximum torque. This can prevent the engine from developing an adequate power during starting of the motor vehicle.
The RPM of a rotary input element of a manually shiftable, automated or automatic transmission (such as a continuously variable transmission known as CVT) can be ascertained on the basis of the transmission ratio and the rotary output element of the transmission (e.g., a shaft which drives the differential of the power train) or by resorting to suitable sensor means.
An object of the invention is to provide a reliable and economical method of operating a torque transmitting system (such as a friction clutch, another clutch or a hydrokinetic torque converter with a bypass clutch) in the power train of a motor vehicle.
Another object of the invention is to provide a method which renders it possible to select an optimum RPM of the output element in the prime mover of a motor vehicle even if the temperature and/or other conditions (such as the elevation above the sea level) are not ideally suited for the utilization of heretofore known automatic operating means for friction clutches and the like.
A further object of the invention is to provide a method which renders it possible to reliably select the extent of engagement of a friction clutch by full consideration of all relevant parameters of the motor vehicle and its power train.
An additional object of the invention is to provide a method which can be practiced in power trains embodying numerous presently known and available components such as a prime mover, a transmission, a friction clutch, one or more actuators for the friction clutch and/or others.
Still another object of the invention is to provide a power train which can be operated in accordance with the above outlined method.
A further object of the invention is to provide a motor vehicle which embodies the above outlined power train and which can operate satisfactorily under circumstances that permit for acceptable operation of vehicles embodying conventional power trains as well as under circumstances which do not allow for a satisfactory utilization of heretofore known power trains.
Another object of the instant invention is to provide a novel and improved computerized control unit which determines the operation of the actuator or actuators for automated torque transmitting systems (such as friction clutches, other types of clutches or hydrokinetic torque converters with bypass or lockup clutches) in the power trains of passenger cars and/or other types of motor vehicles.
An additional object of the present invention is to provide a control unit which can process various signals in a novel and improved way and can transmit appropriate signals to the actuator or actuators for an automated friction clutch or another torque transmitting system.
Still another object of the invention is to provide a novel and improved method of ensuring satisfactory operation of power trains in motor vehicles on terrain well above the sea level and at temperatures which considerably depart from average temperatures.
One feature of the present invention resides in the provision of a method of varying the rate of torque transmission by an adjustable torque transmitting system (such as a friction clutch) in a power train forming part of a motor vehicle and having a prime mover (such as an Otto engine or a Diesel engine) with an output element (such as a camshaft or a crankshaft) rotatable at RPMs at times exceeding and at times below a desired or required optimum RPM. The improved method comprises the steps of monitoring the actual RPM of the output element of the prime mover, reducing the rate of torque transmission by the torque transmitting system when the monitored RPM of the output element of the prime mover is below the desired RPM, and increasing the rate of torque transmission by the torque transmitting system when the monitored RPM of the output element of the prime mover exceeds the desired RPM.
If the method involves varying the rate of torque transmission in a power train wherein the prime mover is subject to variable loads and the torque transmitting system transmits torque to a rotary input element of a mechanical, automated or automatic change-speed transmission, such method can further comprise the steps of generating first signals which denote the monitored RPM of the output element of the prime mover, ascertaining the desired RPM of the output element of the prime mover (this can include monitoring the RPM of the input element of the transmission and generating second signals denoting the monitored RPM of such input element, monitoring the load upon the prime mover and generating third signals which denote the monitored load upon the prime mover, and processing the second and third signals into fourth signals which denote the desired RPM of the prime mover), and generating control signals including processing the first and second signals. The steps of reducing and increasing the rate of torque transmission by the torque transmitting system then preferably include comparing the control signals with the fourth signals.
The step of reducing the rate of torque transmission by the torque transmitting system to the input element of the transmission can further include subtracting the fourth signals from the control signals, and the step of increasing the rate of torque transmission by the torque transmitting system to the input element of the transmission can further include adding the fourth signals to the control signals.
When considered by itself, the step of ascertaining the desired RPM of the output element includes monitoring the actual or momentary RPM of the input element of the transmission and generating signals denoting the monitored RPM of the input element, monitoring the load upon the prime mover and generating additional signals which denote the actual or momentary load upon the prime mover, and processing the first mentioned and additional signals into further signals which denote or represent or are indicative of the desired RPM of the output element of the prime mover.
The aforediscussed method can further comprise the steps of establishing a difference (if any) between the first and fourth signals, and performing upon the fourth signals a gradient limitation in dependency upon two variables (namely (a) the established difference between the first and fourth signals, and (b) the third signals) to thus generate fifth signals. The steps of reducing and increasing the rate of torque transmission by the torque transmitting system then further include comparing the control signals with the fifth signals.
The just mentioned method can be modified by the addition of a further step which includes processing the fifth signals in a regulator to thus generate sixth signals; the steps of reducing and increasing the rate of torque transmission by the torque transmitting system then include comparing the control signals with the sixth signals.
The regulator can be of the type having inputs for the first and fifth signals, and such regulator can be arranged to compare the first and fifth signals and generate the aforementioned sixth signals when the comparison between the first and fifth signals indicates the existence or presence of a difference exceeding a predetermined value.
Alternatively, the regulator can be of the type having inputs for the first and fourth signals, and such regulator can be arranged to compare the first and fourth signals and to generate the sixth signals when the comparison between the first and fourth signals reveals or indicates the existence of a difference exceeding a preselected value.
The regulator can constitute a PI regulator.
It is often preferred to select a regulator having a characteristic which is a function of the monitored RPM of the output element of the prime mover.
If the chosen regulator has adjustable integral and proportional shares, the method can further comprise the step of setting the shares to zero when the monitored RPM of the output element of the prime mover is below a predetermined RPM.
The aforementioned step of generating control signals can include processing the first and second signals (i.e., signals denoting the monitored RPM of the output element of the prime mover, and signals denoting the ascertained RPM of the input element of the transmission) as well as additional signals which are generated by the regulator. Such additional signals can be indicative of the activity of the regulator.
Under certain circumstances, the improved method can comprise the steps of monitoring the RPM of the output element of the prime mover, reducing the rate of torque transmission by the torque transmitting system when the monitored RPM of the output element is below the desired RPM, increasing the rate of torque transmission by the torque transmitting system when the monitored RPM of the output element exceeds the desired RPM, respectively generating first and second signals which denote the monitored RPM and the desired RPM of the output element of the prime mover, and processing the first and second signals. The steps of reducing and increasing the rate of torque transmission by the torque transmitting system then include adjusting the torque transmitting system as a function of the processed first and second signals.
The just mentioned processing step can include subtracting processed second signals from processed first signals when the monitored RPM of the output element of the prime mover is below the desired RPM, and adding processed second signals to processed first signals when the monitored RPM of the output element of the prime mover is above the desired RPM.
Another feature of the invention resides in the provision of a novel and improved power train for a motor vehicle. The power train comprises a prime mover having an output element which is rotatable at a plurality of different RPMs including a desired or optimal or required RPM, an adjustable torque transmitting system (such as a friction clutch) driven by the output element of the prime mover, and means for operating the torque transmitting system. The operating means includes means for monitoring the RPM of the output element of the prime mover, means for comparing the monitored RPM with the desired RPM of the output element of the prime mover, and means for adjusting the torque transmitting system in such a way that the torque being transmitted by the torque transmitting system is being reduced when the monitored RPM of the output element of the prime mover is below the desired RPM and that the torque being transmitted by the torque transmitting system is being increased when the monitored RPM of the output element of the prime mover is above the desired RPM.
The operating means can further comprise means for ascertaining the desired RPM, and such ascertaining means can include means for generating first signals denoting the monitored RPM, means for generating second signals denoting the magnitude of the load upon the prime mover, and means for processing the first and second signals into third signals denoting the desired RPM. Such operating means can further comprise means (such as a PI regulator) for regulating the third signals.
The power train can further comprise a transmission having a rotary input element which receives torque from the torque transmitting system. The operating means of such power train can further comprise means for generating first signals which denote the monitored RPM of the output element of the prime mover, means for monitoring the RPM of the input element of the transmission, means for generating second signals which denote the monitored RPM of the input element of the transmission, means for processing the first and second signals into control signals, and actuator means responsive to the control signals to adjust the torque transmitting system for transmission to the input element of the transmission of a torque which is a function of the control signals.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved power train itself, however, both as to its construction and the modes of assembling and operating the same in accordance with the improved method, together with numerous additional important and advantageous features and attributes thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawings.